Question: What rhymes with siliceous mudstone?
Answer: Nothin' good.
"Audacious home phone"
"Hankering ham bone"
"Silly faces headphone"
"Big paces homegrown"
"Scary fairy sunstone"
Recently, whilst murdering time on the NW Rockhounds page, I came across something wonderful. The most beautiful arrangement of words I had seen in weeks! A fellow hound sought identification for their find, and among the praises and well-mannered debate was a combination of words worthy of conceiving a post: "that's some good old siliceous mudstone." What, in the name of every imaginable ice cream flavor in Heaven, was that about? I had to know. In a blaze of thumb action, I dove further into my internet rabbit hole to a trusted rockossary*. Turns out, I am way better at sniffing out stones than the fossil picker of my childhood, but that's a far throw from having any idea what I'm doing.
Prepare for the grandiose unfurling of that which we all seek in our darkest hour: Answers. Specifically, answers to embarrassingly entry-level gemology questions I have harbored since Day 1 with the NW Rockhounds. But, I will get to that in a minute. What this is, right here, under the quivering anticipation of my dashing fingers, is a post about siliceous mudstone [Figure 1]. It is the titillating product of finding myself at a rare intersection where writer's block met braingasmic discovery. Also, this line up of terms relates directly to a neglected list of adventures I have avoided writing up, so really, this is just scholarly self-indulgence (#bloggerlife). Most unlike me, I failed to elicit my usual brand of puntacitidy* for the title. While at a loss for witty word play, I ultimately went with something that rhymes with siliceous mudstone- in not so many words. Now, without further stalling for introductory anecdotes, on to the terms we learns despite the spurns and burns of braving ferns to get to rocks for which we yearns.
There are some words that, when delicately arranged, transform into poetry. 'Siliceous mudstone' is none of these. The term describes that riveting series of volcanic events where silica rich fluid separates from hotshot magma to create the kind of sexy minerals I'm always frothing at the mouth over. The first part of this title's nomenclature, 'silicaceous,' is the adjectivization* of silica, the base for most of the shinies we're all looking for. My understanding is that 'mudstone' is just a fun way of describing sedimentary minerals with high levels of impurity. Many of these materials are collectively known as that antiquitous gemstone, chalcedony [Figure 2].
Although, I should mention that "chalcedony is not scientifically its own mineral species," [Minerals.net/mineral/chalcedony]. Instead, it is a cryptocrystalline form of quartz whose colloquial use overwhelming refers to white or blue chalcedony [Simon & Schuster's Guide to Rocks & Minerals, page 245]. Technically, the term encompasses agate and jasper, along with many other silicates. This hierarchy of quartz was where I kept tripping up in my use of the word 'jasper.'
This is terribly exciting for one huge, gaping reason: I have been misusing the term jasper and chalcedony since I heard them tumble from the mouth of another rockhound. "Oh," I thought, "this looks kind of like that, everything not agate-ish must be jasper! That means chalcedony is a variant of agate." SoOoooOooOoOooOOOoo painfully incorrect. Why I didn't just look this up months ago and save my tender heart the ache, is unclear. What is clear, is agate (sometimes). If light and/or images pass through a quartz mineral of compacted microcrystalline structure, we generally call it agate, and if the mineral is opaque and no light passes through it, we tend to assume it is jasper [https://rocktumbler.com/blog]. My home rock guide has the following to say about jasper:
"Massive, fine-grained quartz with large amounts of admixed materials, especially iron oxides. The commonest forms are usually strong shades of red, but greyish-green, yellow, or black also occur."
~Simon & Schuster's Guide to Rocks & Minerals, page 245
Having heard jasper referred to as "blood stone," I thought that any sedimentary rocks I found in an area with agate present, were jasper. That's one reason why I hauled a bunch of scoria basalt back from Saddle Mountain. As Billy Joel taught me, "Mistakes are the only thing you can truly call your own." Thanks, Billy, I feel much better about the heap of trash I ditched in the gravel lining that gas station parking lot. That being just one example of many instances that remind me hounding with pros doesn't mean the knowledge and terminology will automatically diffuse into my brains. Science hobbies are a blissful open book to the natural world. But, I digress.
You can see most of the colors described by my guide in the title image, which is a tasty chunk I brought back from a dig this summer [Figure 1]. When you get right down to it, determining agate from jasper from chalcedony comes to one encompassing distinction. Chalcedony is a variety of quartz, instead of the stereotypical well-formed quartz we usually think of [Figure 3]. On the fly, you can tell an agate from a jasper by location and holding it over the light on your phone. Even if you can't see through it when you hold it up to the sun, if light passes through from a source light of any kind, it's not jasper. Agate falls on the translucent and transparent side of one gemstone scale, with jasper leaning attractively on the opaque end. This property scale is known as the diaphaneity of a stone, and it is broken down into three descriptions.
Translucent: light and images pass through
Transparent: light passed through but not images
Opaque: no light passes through
Not the penultimate determinant for a agate and jasper hunt, the diaphanous scale is nonetheless another useful addition to our rockhounding toolkit. Don't even get me started on my frivolous tossing around of the word 'chert.' Although, crazy metamorphic activity is a dead give away for silicates, you and I will need to continue checking our references to classify our finds. Basically, I am eons ahead of where I was hounding this past spring, and am still racing behind the general knowledge base. Thank all the gods in, around, and above us that the pursuit of hobby science is endless. The beauty of this terminological rampage is that now I get to go through and reorganize a fat load of nature booty from this summer [Figure 4]!
Lo, sweet treasures of the Earth, what mysteries will you reveal next?
*Rockossary: Glossary of geologic terms; usually found on the internet
*Adjectivization: when a noun becomes an adjective; the antonym of a nomenalization. Fun fact, apparently there existed no such term for this until now. When I made it up.